doc-gen: update function docs

Author: Chen-Yuan-Lai

docs/source/user-guide/sql/scalar_functions.md

@@ -971,8 +971,8 @@ concat_ws(separator, str[, ..., str_n])
 
 #### Arguments
 
-- **str**: String expression to operate on. Can be a constant, column, or function, and any combination of operators.
 - **separator**: Separator to insert between concatenated strings.
+- **str**: String expression to operate on. Can be a constant, column, or function, and any combination of operators.
 - **str_n**: Subsequent string expressions to concatenate.
 
 #### Example